In the manufacture of optical products “block mounting” or, for short, “blocking” generally denotes the process in which an optical workpiece is temporarily fastened on a so-called “block piece” by a suitable material (low-melting-point alloy or adhesive) or, however, the blocking material is mounted on the workpiece in order itself to form the block piece, which then serves the purpose of holding the workpiece in the respective processing machine and/or coating installation. Correspondingly, in manufacture of optical products “deblocking” defines that process in which the optical workpiece after processing and/or coating thereof is again separated from the block piece or blocking material.
The invention relates particularly to a device and a method for deblocking spectacle lenses. Spectacle lenses are blocked en masse in so-called “RX workshops” before the individual blocked spectacle lens is subjected, at its back or front surface with respect to its optical effect and/or at the edge for fitting in an associated spectacles frame, to machining by a geometrically defined cutter, e.g. milling or turning, or geometrically undefined cutter, e.g. grinding or polishing and/or is coated on its back or front surface in order to achieve additional effects, for example increase in scratch resistance, anti-reflection properties, vapor deposition, or hydrophobic characteristics.
If in the following reference is generally made in connection with the present invention to “spectacle lenses” as preferred field of use then there are to be understood by that optical lenses or lens blanks for spectacles from customary materials, such as polycarbonate, mineral glass, CR 39, HI Index, etc., and with any beginning shape of the circumferential edge of the lens or the lens blank, which prior to blocking can already have been—but does not have to be—subjected to pre-processing or pre-coating at one optically effective surface or both optically effective surfaces or at the edge. In addition, the spectacle lens can be provided on its surface at which it is or will be blocked with a film, a lacquer or the like in order to protect this surface from contamination and damage and/or to improve the adhesion characteristics between spectacle lens and blocking material, without this actually being specified hereinbelow.
There is no lack of proposals in the prior art with regard to how a device for automated deblocking of spectacle lenses can be constructed, in which connection a pressure medium, for example, water is employed in order to detach the spectacle lens from the block piece by application of hydraulic force and, in particular, either from inside by way of a pressure medium channel in the block piece, which opens at the blocking surface of the block piece facing the spectacle lens (e.g. DE 10 2005 038 063 A1, FIG. 13; WO 03/018253 A1, FIG. 4) or from outside by use of a high-pressure water jet which is issued by a nozzle and which impinges on an edge location between block piece and spectacle lens (for example WO 2008/003805 A1, FIG. 1).
A disadvantage of the inside application of the hydraulic forces is to be seen in that the block piece is provided with cavities which are open towards the blocking surface and which stand in the way of a desirable whole-area support of the spectacle lens at the block piece. In principle, the opening in the blocking surface can indeed be reduced in order to achieve an approximately whole-area support, but then it is barely possible to apply the hydraulic forces in order to separate the spectacle lens from the block piece.
Help can admittedly be created here through the use of a small piston in the separate block piece, which adjoins the blocking surface, as proposed as an alternative in WO 03/018253 A1 as shown in FIGS. 14 to 22. However, during the deblocking, mechanical forces are then applied by way of this piston to a relatively small central area at the spectacle lens, which can have the consequence of destroying the spectacle lens. It is at least necessary for the detaching to generate forces which are higher than the adhesion forces between spectacle lens and block piece. In the case of the afore-described piston solution the separating forces act on the center of the spectacle lens, whereas the adhesion forces primarily act in an annular zone at the spectacle lens edge. Particularly in the case of thin spectacle lens this can have the consequence of comparatively strong deformations and high levels of stress in the spectacle lens to be deblocked, which ultimately can produce fracture of the spectacle lens, quite apart from the outlay involved in providing such a piston in the block piece.
The previously known outside solution according to WO 2008/003805 A1, does indeed enable whole-area support of the spectacle lens at the block piece and additionally reduces the risk of damage of the spectacle lens during deblocking. However, this prior art is in need of improvement in another respect.
The deblocking method disclosed there was developed specifically for deblocking spectacle lenses blocked by a thermoplastic blocking material. In that case melting of the blocking material is initially imposed by immersing the composite of spectacle lens, blocking material and block piece in a bath with hot water. Block piece and blocking material as well as a protective film on the spectacle lens are then detached from the spectacle lens by a high-pressure water jet. For that purpose the water for the jet is heated to a temperature of between 50° C. and 65° C. in order to re-soften the blocking material and ultimately liquefy it as a consequence of the heating. The high-pressure water jet here fans out relatively widely and is in addition rotated about the longitudinal axis of the nozzle in order to also pass under the protective foil on the rotating spectacle lens and lift this off the spectacle lens.
A disadvantage of this prior art is to be seen particularly in that—also a consequence of the intermediate preheating step in the hot water bath—the deblocking of a spectacle lens takes a relatively long time, which represents an obstacle to efficient use of this method in RX workshops.
What is needed is a device for deblocking optical workpieces, particularly spectacle lenses, by which the optical workpieces can be deblocked as safely, free of damage and rapidly as possible. What is also needed is a corresponding deblocking method.